Population studies have provided evidence for an inverse relationship between plasma high density lipoprotein (HDL) cholesterol levels and the prevalence and incidence of ischemic heart disease. Furthermore, metabolic studies showing changes in HDL levels by means of drugs, diet, hormones, exercise, weight loss, etc., indicate that a particular subfraction of HDL, namely HDL2b, is responsibe to intervention; the relationship between HDL2b and HDL2a and HDL3 remains unclear. The purpose of the present proposal is to understand these relationships by utilizing normal male and female subject and a diet which is known to alter HDL levels. The studies will be carried out in a Clinical Research Center. The isocaloric diets will include changes in carbohydrate and fat; dietary cholesterol and P/S ratio will remain constant. Particular attention will be given to changes in the HDL subfractions as they relate to changes in post-heparin plasma hepatic triglyceride lipase and lipoprotein lipase and adipose tissue lipoprotein lipase. The methods include standardized procedures for quantitation of plasma lipids, apoproteins A-I, A-II, C-II, C-III and E, and techniques for measuring HDL subfractions including gradient gel electrophoresis and zonal ultracentrifugation. The long-term goal of the study is to define the mechanisms whereby lipoprotein lipase and hepatic triglyceride lipase alter the plasma levels of HDL-cholesterol.